Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
In a fan-out wafer level chip scale package (FO-WLCSP), a semiconductor die is typically electrically connected to a build-up interconnect structure and covered by an encapsulant. The encapsulant is disposed between a majority of the surface area between the semiconductor die and build-up interconnect structure. The encapsulant is often thermally non-conductive so heat generated by the semiconductor die is not effectively dissipated through the interconnect structure. Without effective heat dissipation, the generated heat can reduce performance, decrease reliability, and reduce the useful lifetime of the semiconductor device.
In addition, any mismatch in the coefficient of thermal expansion (CTE) between the encapsulant, semiconductor die, and build-up interconnect structure induces thermal stress which can cause defects in the interconnect joints. The thermal stress can also cause warpage during encapsulation or after the package is completely formed. An underfill material beneath the semiconductor die can absorb stress; however, the underfill material is typically thermally non-conductive so heat dissipation remains an issue.
The semiconductor die are known to shift during encapsulation. One solution to die shifting is to form wettable contact pads over a temporary carrier. The die bumps are bonded to the wettable contact pads to reduce die shifting during encapsulation. However, forming the wettable contact pads increases contact resistance, reduces electrical performance, and increases manufacturing costs.
As the dimensions of the semiconductor die become smaller and demands for higher pin count increases, the bump size and pitch must be reduced. The smaller bumps increase void formation since the gap between the semiconductor die and temporary carrier is too narrow to allow uniform underfilling.